Combined angioplasty and intravascular radiotherapy method and apparatus

ABSTRACT

Apparatus and methods are provided for relieving a stenosed region of a blood vessel such as a coronary artery using a single catheter that relieves the angioplasty by conventional means and then delivers an easily controllable inherently uniform dosage of radiation to the walls of a blood vessel for preventing restenosis after angioplasty. An embodiment of the apparatus comprises a catheter having an angioplasty balloon that is inflatable with a liquid containing a suspended radioactive material such as  125  I or  32  P. The balloon is surrounded by a membrane to capture the radioactive liquid in the event the balloon ruptures. The catheter is advanced through the patient until the balloon is disposed in the stenosed region of the blood vessel. The stenosed region is relieved using the angioplasty balloon, after which the angioplasty balloon is emptied and re-filled with the radioactive liquid, which expands the balloon to engage the walls of the blood vessel thereby providing an inherently uniform dosage of radiation to the blood vessel walls. 
     Another embodiment of the apparatus comprises a catheter having an angioplasty balloon surrounded by a radiotherapy treatment balloon that is separately inflatable with a radioactive liquid. The stenosed region is relieved using the inner angioplasty balloon after which the radiotherapy treatment balloon is filled with the radioactive liquid. An additional containment balloon outside the radiotherapy treatment balloon may also be provided to prevent loss of radioactive liquid in the event the treatment balloon ruptures. The angioplasty balloon may be partly filled during the radiation treatment to minimize the volume of radioactive liquid necessary to achieve the desired dosage.

This is a continuation of U.S. application Ser. No. 08/386,419, filedFeb. 10, 1995, now U.S. Pat. No. 5,662,580 which is acontinuation-in-part of U.S. application Ser. No. 08/352,318 filed Dec.8, 1994, now U.S. Pat. No. 5,616,114.

BACKGROUND OF THE INVENTION

This invention relates generally to treatment of selected tissue byinter-vivo radiation, specifically to radiation treatment of traumatizedregions of the cardiovascular system to prevent restenosis of thetraumatized region, more specifically to radiation treatment to preventrestenosis of an artery traumatized by percutaneous transluminalangioplasty (PTA).

PTA treatment of the coronary arteries, percutaneous transluminalcoronary angioplasty (PTCA), also known as balloon angioplasty, is thepredominant treatment for coronary vessel stenosis. Approximately300,000 procedures were performed in the United States (U.S.) in 1990and an estimated 400,000 in 1992. The U.S. market constitutes roughlyhalf of the total market for this procedure. The increasing popularityof the PTCA procedure is attributable to its relatively high successrate, and its minimal invasiveness compared with coronary by-passsurgery. Patients treated by PTCA, however, suffer from a high incidenceof restenosis, with about 35% of all patients requiring repeat PTCAprocedures or by-pass surgery, with attendant high cost and addedpatient risk. More recent attempts to prevent restenosis by use ofdrugs, mechanical devices, and other experimental procedures have hadlimited success.

Restenosis occurs as a result of injury to the arterial wall during thelumen opening angioplasty procedure. In some patients, the injuryinitiates a repair response that is characterized by hyperplastic growthof the vascular smooth muscle cells in the region traumatized by theangioplasty. The hyperplasia of smooth muscle cells narrows the lumenthat was opened by the angioplasty, thereby necessitating a repeat PTCAor other procedure to alleviate the restenosis.

Preliminary studies indicate that intravascular radiotherapy (IRT) haspromise in the prevention or long-term control of restenosis followingangioplasty. It is also speculated that IRT may be used to preventstenosis following cardiovascular graft procedures or other trauma tothe vessel wall. Proper control of the radiation dosage, however, iscritical to impair or arrest hyperplasia without causing excessivedamage to healthy tissue. Overdosing of a section of blood vessel cancause arterial necrosis, inflammation and hemorrhaging. Underdosing willresult in no inhibition of smooth muscle cell hyperplasia, or evenexacerbation of the hyperplasia and resulting restenosis.

U.S. Pat. No. 5,059,166 to Fischell discloses an IRT method that relieson a radioactive stent that is permanently implanted in the blood vesselafter completion of the lumen opening procedure. Close control of theradiation dose delivered to the patient by means of a permanentlyimplanted stent is difficult to maintain because the dose is entirelydetermined by the activity of the stent at the particular time it isimplanted. Additionally, the dose delivered to the blood vessel isnon-uniform because the tissue that is in contact with the individualstrands of the stent receive a higher dosage than the tissue between theindividual strands. This non-uniform dose distribution is especiallycritical if the stent incorporates a low penetration source such as abeta emitter.

U.S. Pat. No. 5,302,168 to Hess teaches use of a radioactive sourcecontained in a flexible carrier with remotely manipulated windows. H.Bottcher, et al. of the Johann Wolfgang Goerhe University MedicalCenter, Frankfurt, Germany report in November 1992 of having treatedhuman superficial femoral arteries with a similar endoluminal radiationsource. These methods generally require use of a higher activity sourcethan the radioactive stent to deliver an effective dose. Accordingly,measures must be taken to ensure that the source is maintainedreasonably near the center of the lumen to prevent localizedoverexposure of tissue to the radiation source. Use of these higheractivity sources also dictates use of expensive shielding and otherequipment for safe handling of the source.

The aforementioned application Ser. No. Ser. No. 08/352,318,incorporated herein by reference, discloses IRT methods and apparatusfor delivering an easily controllable uniform dosage of radiation to thewalls of the blood vessel without the need for special measures tocenter the radiation source in the lumen, the need for expensiveshielding to protect medical personnel, or the need for expensive remoteafterloaders to handle the higher activity sources. This is accomplishedby introducing a radioactive liquid into a balloon catheter to expandthe balloon until it engages the blood vessel walls. The aforementionedapplication also discloses methods and apparatus for relieving thestenosed region of the blood vessel and performing the IRT procedurewith a single apparatus, which may include an angioplasty balloon with aseparately inflatable outer IRT balloon.

In certain applications, however, the size of the blood vessel is toosmall to admit a catheter with a profile large enough to accommodateseparate inflation lumens for an outer and inner balloon. A smallerprofile IRT catheter be obtained, however, by eliminating the IRTinflation lumen, thereby converting the outer IRT balloon to acontainment membrane.

Where the blood vessel size permits, a further advantage may beobtained, if a combination angioplasty and IRT catheter includes meansfor extending the IRT treatment area beyond the angioplasty treatmentarea to irradiate a region extending proximal and distal of theangioplasty treatment area. By providing for IRT treatment that covers awider area than the angioplasty treatment area, all of the tissuetraumatized by the angioplasty is irradiated with the measured dosage,even if the catheter is displaced between the angioplasty and IRTprocedures. Accordingly, proper inhibition of smooth muscle cellhyperplasia is more reliably achieved.

SUMMARY OF THE INVENTION

According to the present invention, a single treatment catheter is usedto perform all, or at least the final stage, of the angioplastyprocedure and to perform the entire IRT procedure. In an embodiment ofthe present invention, the treatment catheter comprises a flexibleelongate member having an angioplasty balloon that is surrounded by anIRT treatment balloon having a separate inflation lumen. The catheter isadvanced through the cardiovascular system of the patient until theballoons are positioned at a target area comprising the stenosed regionof the blood vessel. The stenosis is first relieved using the innerangioplasty balloon, then the target tissue is irradiated by filling theIRT treatment balloon with a radioactive liquid until the outer wall ofthe balloon gently engages the inner wall of the blood vessel.

The radioactive liquid comprises a suspension of a beta emittingmaterial such as ³² P or a photon emitting material such as ¹²⁵ I in aliquid carrier. The radiation emitted by such sources is quicklyabsorbed by surrounding tissue and will not penetrate substantiallybeyond the walls of the blood vessel being treated. Accordingly,incidental irradiation of the heart and other organs adjacent to thetreatment site is substantially eliminated. Because the radioactiveliquid has a substantially uniform suspension of radioactive material,the radiation emitted at the surface of the balloon in contact with thetarget area of the blood vessel is inherently uniform. Accordingly,uniform irradiation of the blood vessel wall is also inherent.

According to an embodiment of the present invention, the outer IRTtreatment balloon is made longer than the inner angioplasty balloon.Accordingly, when filled, the IRT treatment balloon will irradiate asection of the blood vessel that extends on both sides beyond the areatreated with the angioplasty balloon. This extended IRT treatment areaprovides a margin of safety to ensure that, even if the catheter shiftsslightly during the treatment, the entire traumatized region of theblood vessel will be treated to prevent smooth muscle cell hyperplasia.

The catheter of the present invention may also be equipped withperfusion ports proximal and distal of the balloon to permit blood flowpast the balloon when inflated.

According to another embodiment of the present invention, a thirdballoon is provided that completely envelopes the IRT treatment balloon.This containment balloon acts as a containment vessel in the event theIRT treatment balloon ruptures when filled with the radioactive liquid.In use, prior to filling the treatment balloon with the radioactiveliquid, the containment balloon is filled, preferably with a non-toxicradio-opaque fluid, to verify the integrity of the containment balloon.The radio-opaque fluid filled containment balloon may also be used toverify correct positioning of the catheter within the target area of theblood vessel.

After the angioplasty procedure is performed, the angioplasty balloonmay be deflated, or left partially inflated. Leaving the angioplastyballoon partially inflated reduces the amount of radioactive liquid thatmust be used to fill the treatment balloon by occupying space within theIRT treatment balloon. Because of the self-attenuation of theradioactive liquid itself, most of the radioactivity originates at thesurface of the treatment balloon. Accordingly, the surface radiation isnot reduced substantially as a result of the center being filled with aninert material.

According to another embodiment of the present invention, a proximal anddistal blocking balloon are also provided to contain the radioactiveliquid in the target area in the event of a total failure of allcontainment systems.

According to another embodiment of the present invention, where a verylow profile is required to access small blood vessels, the cathetercomprises an inner angioplasty balloon and an outer balloon, however,the outer balloon inflation lumen is eliminated, thereby converting theouter balloon to a containment membrane. The IRT procedure is thencarried out by filling the angioplasty balloon itself with theradioactive liquid after the angioplasty procedure has been performed.The containment membrane contains the radioactive liquid in the unlikelyevent that the angioplasty balloon, which previously withstoodangioplasty pressures, ruptures under the more moderate IRT pressure.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, aspects, features and attendant advantagesof the present invention will become apparent from a consideration ofthe ensuing detailed description of presently preferred embodiments andmethods thereof, taken in conjunction with the accompanying drawings, inwhich:

FIGS. 1A-1C are plan and cross sectional views of an apparatus accordingto the present invention;

FIGS. 2A-2C are plan and cross sectional views of an alternateembodiment of an apparatus according to the present inventionincorporating a containment balloon; and

FIGS. 3A-3C are plan and cross sectional views of an alternateembodiment of an apparatus according to the present inventionincorporating proximal and distal blocking balloons.

FIGS. 4A-4C are plan and cross sectional views of an alternateembodiment of an apparatus according to the present invention comprisinga low profile catheter with a containment membrane.

DESCRIPTION OF PREFERRED EMBODIMENTS AND METHODS

FIGS. 1A and 1B illustrate a suspended-isotope IRT catheter according tothe present invention. The IRT catheter comprises shaft 10 having anangioplasty inflation lumen 11, IRT inflation lumen 12, a conventionallyformed tip that seals the end of the inflation lumens, and may includelongitudinal guidewire/injection/perfusion lumen 14 which passes throughthe tip. Shielded injector 16, which may be a manual or automatedsyringe containing a radioactive liquid 30, or a pump connected to areservoir of radioactive liquid 30, is connected to the proximal end ofshaft 10 and is in fluid communication with IRT inflation lumen 12. Toprevent possible spillage and corresponding radioactive contamination ofthe operating room and/or its personnel, the shielded injector 16 ispermanently attached to shaft 10, or preferably, injector 16 is equippedwith a fail-safe non-detachable connector 18, which cannot be detachedfrom the corresponding receptacle 20 of shaft 10 once it is attachedthereto. Non-detachable connector 18 also prevents the radioactiveliquid 30 from being discharged from injector 16 until the connector isconnected to the receptacle in shaft 10. Connectors having ring-detentsand other non-detachable fluid fittings are well known in the art, asare piercing valves and other common methods of preventing fluid flowprior to attachment of a fluid fitting. The proximal end of shaft 10also includes angioplasty luer fitting 15 in fluid communication withangioplasty inflation lumen 11, and guidewire lumen luer fitting 17 influid communication with guidewire lumen 14, through which drugs may beinjected directly into the patient's blood stream.

FIG. 1C is an enlarged view of the distal end of the present embodimentof the catheter. Angioplasty balloon 32 comprises a conventional elasticor preferably an inelastic balloon, which may preferably be made frompolyethylene terephthalate (PET), polyvinyl chloride (PVC), or othermedical grade material suitable for constructing a strong non-compliantballoon. Angioplasty balloon 32 is in fluid communication withangioplasty inflation lumen 11 via ports 34. Immediately inside proximaland distal ends of balloon 32 are markers 36, comprising bands of silveror other suitable x-ray opaque material. Markers 36 aid in the properpositioning of angioplasty balloon 32 within the target area of theblood vessel under fluoroscopy.

IRT Treatment balloon 42 is disposed at the distal end of shaft 10surrounding angioplasty balloon 32. IRT treatment balloon is an elasticor preferably an inelastic balloon, which may preferably be made frompolyethylene terephthalate (PET), polyvinyl chloride (PVC), or othermedical grade material suitable for constructing a strong non-compliantballoon. IRT treatment balloon 42 is sealed at its proximal and distalends to catheter shaft 10 in fluid communication with inflation lumen 12via inflation lumen ports 44.

Immediately adjacent to and outside the ends of IRT treatment balloon 42are perfusion ports 48, which are in fluid communication with guidewirelumen 14. Perfusion ports are well known in the art as a means ofpermitting some blood flow past a balloon that is inflated within andotherwise blocking a blood vessel.

In operation, an appropriately sized catheter according to the presentinvention is selected and positioned within the patient's blood vesselby conventional means so that the balloon is within the target areacomprising the stenosed region of the blood vessel. The stenosis isrelieved by inflating the angioplasty balloon according to conventionalmethods. After the angioplasty procedure has been performed, shieldedinjector 16 is connected to the receptacle at the proximal end of thecatheter shaft and the air evacuated from the IRT treatment balloon andthe inflation lumen. In the case of a shielded syringe, this is donesimply by withdrawing the plunger. The balloon is then filled with theliquid containing the suspended isotope until the outer wall of theballoon gently engages the inner wall of the blood vessel. The balloonis maintained in this inflated state for a predetermined period of timecalculated to deliver an effective dose of radiation to the wall of theblood vessel. The radioactive liquid is then withdrawn from the balloonand the catheter withdrawn from the patient's body.

To reduce the chances of overpressurizing the treatment balloon andcausing a rupture, pressure feedback device 22 is connected to theproximal end of inflation lumen 12. Pressure feedback device 22 may be apressure gauge, or preferably a solid-state pressure transducer, whichin the in the event an overpressure condition is detected, operates analarm 24 and/or a waste gate 26 that discharges the inflation lumen 12into a shielded container. Alternately, the solid state pressuretransducer may be positioned at the distal end of the inflation lumen tomonitor pressure in the balloon directly.

For added safety, prior to filling IRT treatment balloon withradioactive liquid, IRT treatment balloon may be filled with a commonlyused non-toxic radio-opaque contrast medium to verify integrity of theIRT treatment balloon. Once the integrity is verified, the contrastmedium would be evacuated and shielded syringe 16 connected to thereceptacle at the proximal end of the catheter shaft. Although the smallamount of contrast medium that would remain in the IRT treatment balloonwould dilute the radioactive liquid, the amount of dilution would bemeasurable and could be compensated.

FIGS. 2A-2C illustrate an alternate embodiment of the present inventionfurther including an outer containment balloon 52. Containment balloon52 is an inelastic or preferably an elastic balloon, which is preferablymade of latex or other medical grade material suitable for constructingpuncture-resistant elastic balloons. Containment balloon 52 is attachedat its proximal and distal ends to shaft 10 and completely surroundstreatment balloon 32. Containment balloon 52 is in communication withcontainment balloon inflation lumen 54 via containment balloon inflationlumen port 56, which in turn is in fluid communication with containmentballoon luer fitting 58 at the proximal end of shaft 10.

In operation, after the IRT catheter is in position, but before IRTtreatment balloon 42 is filled with the radioactive liquid, containmentballoon 52 is filled with a commonly used non-toxic radio-opaquecontrast medium injected through containment balloon luer fitting 58.The integrity of containment balloon is verified by fluoroscopy,pressure, or other suitable means and, if integrity is confirmed, theradio-opaque liquid is withdrawn and the procedure for injecting theradioactive liquid into treatment balloon 42 carried out. If theintegrity of the containment balloon has been compromised (for exampleby sharp edges in guide catheters, guide wires, stents, etc.) a newcatheter is selected and repositioned. By verifying integrity of thecontainment balloon after the balloon is in position, but before theradioactive liquid is injected, a substantial degree of safety againstaccidental injection of radioactive liquid into the patient's bloodstream is achieved. Where a containment balloon is used (or blockingballoons as discussed with reference to FIGS. 3A-3C are used), pressurefeedback device 22 may also be used to activate an emergency evacuationsystem. In the event the pressure feedback device detected a sudden dropin pressure (indicating rupture of the treatment balloon) the pressurefeedback device would initiate an immediate withdrawal of allradioactive liquid from the patient, for example by opening a valve to ashielded vacuum accumulator 28.

Several important considerations must be balanced in the design of anapparatus for safely and effectively injecting a radioactive liquid intoa patient to irradiate a blood vessel to prevent restenosis. Although¹²⁵ I and ³² P are both emitters of low penetrating radiation suitablefor use according to the present invention, ³² P is preferred because ithas a half-life of only 14.3 days as compared with the 60 day half-lifeof ¹²⁵ I. A shorter half life renders ³² P safer to use because, in theevent of a catastrophic failure involving leakage of radioactive liquidinto the patient's blood stream, for a given calculated dose rate, ashorter half life will result in a lesser total body dosage. ³² P isalso a relatively pure beta radiation emitter. ³² P has been used in thetreatment of chronic leukemia, where it is injected directly into apatient's blood stream. Accordingly, substantial medical knowledgeexists as to the effects of ³² P in the blood stream.

In the leukemia treatment, depending on the patient's weight, asuspended radiation source of about 6 to 15 millicuries of ³² P is used.Accordingly, for maximum safety, the preferred suspended-isotope IRTcatheter should also use a source of no more than 6 millicuries. Priorexperiments have shown that a dose of about 1000 to 3500 rads deliveredto the blood vessel wall from a gamma radiation source is effective toinhibit the smooth muscle cell hyperplasia that causes restenosis. Forlow penetration sources, such as beta radiation emitters, it is believeda dosage up to 5,000 rads may be tolerated. For a 6 millicurie ³² Psource to deliver such a dose to the surface of the blood vessel, theballoon must be in position for substantially in excess of one minute,thus necessitating the perfusion ports.

For example, it is estimated that the balloon will absorb approximately15% of the radiation delivered by the radioactive liquid. Accordingly,to deliver 2000 rads to the blood vessel wall, 2350 rads must bedelivered to the inner wall of the balloon. A typical treatment ballooncomprises a cylindrical balloon having an internal diameter of 3millimeters, a length of about 30 millimeters, and an interior volume ofapproximately 0.2 cubic centimeters. Accordingly, to limit the totalsource to no more than 6 millicuries, 0.2 cubic centimeters of a liquidhaving a source concentration of no more than 30 millicuries per cubiccentimeter must be used. A 30 millicurie per cubic centimeter source,however, requires about 6 minutes to deliver 2350 rads to the interiorof the 3 millimeter diameter treatment balloon and thus requires about 6minutes to deliver 2000 rads to the interior wall of the blood vessel.

The larger the balloon, the lower the concentration of the radiationsource in the liquid must be to maintain the safe limit of 6millicuries. However, the lower the concentration, the lower the doserate and the longer the balloon must remain inflated to deliver aneffective dose to the blood vessel wall.

To reduce the volume of radioactive liquid that must be used,angioplasty balloon 32 may be left partially or substantially filledduring the IRT treatment. Because the liquid near the center of a bodyof radioactive liquid does not contribute significantly to the radiationemitted from the surface of the body, by leaving the angioplasty balloonpartially filled in the center of the IRT treatment balloon, a smallervolume of radioactive liquid can be used without significantly affectingthe radiation delivered to the vessel wall. Without the angioplastyballoon acting as an inert filler, to avoid exceeding the 6 millicurielimit, the same size treatment balloon would require a larger volume oflower concentration radioactive liquid, with a commensurately lower doserate and longer required treatment interval.

FIGS. 3A-3C illustrate an additional embodiment of the present inventionincorporating blocking balloons 62. Blocking balloons 62 are inelasticor preferably elastic balloons, which are preferably made of latex orother medical grade material suitable for constructingpuncture-resistant elastic balloons. Blocking balloons 62 are sealed toshaft 10 proximal and distal of treatment balloon 42 between perfusionports 48, and are in fluid communication with a common blocking ballooninflation lumen 64 via blocking balloon inflation ports 66. Blockingballoon inflation lumen 64 is, in turn, in fluid communication withblocking balloon luer fitting 68 at the proximal end of shaft 10.

In operation, after the angioplasty procedure is completed, blockingballoons 62 are inflated in the blood vessel until the blood flow pastthe balloons is substantially stopped (the flow of blood in the vesselitself continues through the perfusion ports). The treatment balloon 42is then inflated with the radioactive liquid for treatment of the bloodvessel walls. In the event treatment balloon 42 ruptures and, wherepresent, containment balloon 52 also fails, the radioactive liquid isstill contained in the blood vessel between blocking balloons 62. Theradioactive liquid can then be withdrawn either through any of theinflation lumens that, because of the breach, are in fluid communicationwith the interior of the blood vessel between the blocking balloons 62,or preferably withdrawn automatically using the emergency evacuationsystem discussed with reference to FIGS. 2A-2C. Blocking balloons mayalso be used in lieu of containment balloon 52, especially inparticularly small lumens where a smaller profile is desirable.

FIGS. 4A-C illustrate an embodiment of the present invention for use inblood vessels that are too small to admit a catheter having a profilelarge enough to support independent inflation lumens for an angioplastyand an IRT balloon. The reduced-profile IRT catheter comprises shaft 10having a single multi-purpose inflation lumen 81, a conventionallyformed tip that seals the end of the inflation lumens, and may includelongitudinal guidewire/injection/perfusion lumen 14 which passes throughthe tip.

FIG. 4C is an enlarged view of the distal end of the embodiment of thecatheter. Angioplasty balloon 32 comprises a conventional elastic orpreferably an inelastic balloon, which may preferably be made frompolyethylene terephthalate (PET), polyvinyl chloride (PVC), or othermedical grade material suitable for constructing a strong non-compliantballoon. Angioplasty balloon 32 is in fluid communication withmulti-purpose inflation lumen 81 via ports 84. Preferably, angioplastyballoon 32 is surrounded by IRT containment membrane 92, which is sealedto catheter shaft 10.

In a preferred method of operation, after the distal end of the catheteris properly positioned in a stenosed region of the blood vessel,angioplasty balloon 32 is filled with a non-toxic fluid contrast mediuminjected through fitting 20 by means of an injector that mates with, butis detachable from fitting 20. The fluid is injected until angioplastyballoon 32 expands the stenosed region to an appropriate size. The fluidis then evacuated and, preferably, inflation lumen 81 exposed to avacuum to remove as much of the fluid contrast medium as possible.Balloon 32 is then filled with radioactive liquid 30 until the walls ofthe balloon engage the walls of the blood vessel. The balloon ismaintained in this inflated state for a predetermined period of timecalculated to deliver an effective dose of radiation to the wall of theblood vessel. The radioactive liquid is then withdrawn from the balloonand the catheter withdrawn from the patient's body. A small amount ofcontrast medium will remain in balloon 30 after the angioplastyprocedure to dilute the radioactive liquid. However, the dilution may becompensated, by increasing the initial concentration of the radioactiveliquid or, preferably by increasing the treatment interval. Thecontainment membrane 92 contains the radioactive liquid in the event theangioplasty balloon ruptures when filled with the radioactive liquid.

Thus, the present invention provides safe and effective method andapparatus for combining angioplasty and restenosis prevention into asingle apparatus capable of relieving angioplasty and delivering aneasily controllable inherently uniform dosage of radiation to controlrestenosis in the region of the blood vessel traumatized by theangioplasty procedure.

Although certain preferred embodiments and methods have been disclosedherein, it will be apparent from the foregoing disclosure to thoseskilled in the art that variations and modifications of such embodimentsand methods may be made without departing from the true spirit and scopeof the invention. Accordingly, it is intended that the invention shallbe limited only to the extent required by the appended claims and therules and principles of applicable law.

What is claimed is:
 1. Apparatus for localized intravascularradiotherapy (IRT) of a blood vessel, such as a coronary artery,comprising:a catheter comprising an elongate member having a proximalend and a distal end, said elongate member being sized and of sufficientflexibility to be introduced into a patient's body through a lumen ofthe patient's vascular system until the distal end is disposed at atarget area within the blood vessel, said elongate member having firstand second inflation lumens with respective openings adjacent theproximal end thereof; an angioplasty balloon secured to the distal endof said elongate member, said angioplasty balloon having an interiorchamber in fluid communication with the first inflation lumen of theelongate member to admit fluid into said interior chamber for sufficientpressurization thereof to enable use of the angioplasty balloon toperform an angioplasty procedure on a region of stenosis in said targetarea of the blood vessel; an IRT treatment balloon secured to the distalend of said elongate member, said IRT treatment balloon having aninterior chamber surrounding said angioplasty balloon and in fluidcommunication with the second inflation lumen of the elongate member toadmit radioactive fluid into the interior chamber of the IRT treatmentballoon after de-pressurizing the angioplasty balloon following theangioplasty procedure, for exposure of the wall of said blood vessel insaid target area to said IRT by filling the interior chamber of said IRTtreatment balloon with a sufficient quantity of radioactive fluid tocause said IRT treatment balloon to gently engage the inner wall of theblood vessel thereat after the angioplasty procedure; and means forevacuating radioactive fluid from said IRT treatment balloon promptlyafter said IRT treatment balloon has been maintained in place for aperiod of time calculated to deliver an effective dose of radiation tothe wall of said blood vessel in said target area, whereby to cause saidIRT treatment balloon to collapse to enable withdrawal thereof from thepatient's vascular system together with said catheter.
 2. The apparatusof claim 1, further including means for monitoring pressure in said IRTtreatment balloon to initiate immediate withdrawal of radioactive fluidtherefrom in the event of a sudden drop in pressure therein.
 3. Theapparatus of claim 1, further including radiation-shielded means coupledto said proximal opening for the second inflation lumen to introduceradioactive fluid into the interior chamber of the IRT treatmentballoon.
 4. The apparatus of claim 3, wherein a radioactive fluidemployed to fill the interior chamber of the IRT balloon comprises asuspension of particles of a beta emitter in a liquid carrier.
 5. Theapparatus of claim 4, wherein the beta emitter is an isotope ofradioactive phosphorus.
 6. The apparatus of claim 3, wherein aradioactive fluid employed to fill the interior chamber of the IRTtreatment balloon comprises a suspension of particles of a photonemitter in a liquid carrier.
 7. The apparatus of claim 6, wherein thephoton emitter is an isotope of radioactive iodine.
 8. The apparatus ofclaim 1, further including perfusion means for enabling blood to flowpast the distal end of the catheter when the IRT treatment balloon isinflated.
 9. The apparatus of claim 1, further including a containmentballoon secured to the distal end of the elongate member andencompassing the IRT treatment balloon within an interior chamber of thecontainment balloon, to capture any radioactive fluid escaping from theIRT treatment balloon.
 10. A method for performing a combinedangioplasty procedure and localized intravascular radiotherapy (IRT) ofa stenosed region of a blood vessel of a patient, comprising the stepsof:inserting into a lumen of the patient's cardiovascular system acatheter in the form of an elongate member having attached thereto atits distal end at least a first balloon and a second balloonencompassing said first balloon, each of said first and second balloonsbeing independently inflatable with its own respective inflation lumenrunning from a point adjacent the proximal end of the elongate memberand therethrough into the interior chamber of the respective balloon,the elongate member with attached balloons being of a size andflexibility suitable for insertion into and advancement through aluminal path of the cardiovascular system to position the distal end ofthe elongate member at said stenosed region of the blood vessel;advancing the elongate member through said luminal path to position theballoons attached to the distal end at the stenosed region; performingan angioplasty procedure by inflating the first balloon to exertsufficient pressure on the inner wall of the blood vessel to relieve thestenosis in said region thereof, whereby to open the lumen of the bloodvessel thereat sufficiently for adequate blood flow therethrough, andthen de-pressurizing the first balloon; inflating the second balloonafter the first balloon is at least partially collapsed, by introducinga sufficient quantity of radioactive fluid into the interior chamber ofthe second balloon to urge the balloon membrane thereof into gentleengagement with the inwardly facing surface of the blood vessel in theregion thereof subjected to the angioplasty procedure; leaving theradioactive liquid-filled second balloon in said gentle engagement for apredetermined period of time sufficient to deliver an effective dose ofradiation to the blood vessel wall in the region thereof subjected tothe angioplasty procedure; withdrawing said radioactive liquid from thesecond balloon immediately upon expiration of said predetermined periodof time to preclude substantial additional irradiation of the bloodvessel wall in said region and to allow the second balloon to collapse;and after said second balloon has collapsed sufficiently, retracting thecatheter from the patient.
 11. The method of claim 10, wherein theradioactive liquid introduced into the interior chamber of the secondballoon comprises a suspension of particles of a beta emitter in aliquid carrier.
 12. The method of claim 11, wherein the beta emitter isan isotope of radioactive phosphorus.
 13. The method of claim 10,wherein the radioactive liquid introduced into the interior chamber ofthe second balloon comprises a suspension of particles of a photonemitter in a liquid carrier.
 14. The method of claim 13, wherein thephoton emitter is an isotope of radioactive iodine.
 15. The method ofclaim 10, further including the step of introducing a sufficientquantity of a contrast medium into the interior chamber of the secondballoon to test the integrity of the membrane thereof, beforeintroducing radioactive liquid into the interior chamber thereof. 16.The method of claim 10, further including providing for perfusion pastthe distal end of the catheter at least while the second balloon isinflated, to enable adequate blood flow to avoid infarction during thegentle engagement of the membrane of the second balloon with theinwardly facing surface of the blood vessel.
 17. The method of claim 10,wherein the catheter includes a containment sheath secured to the distalend of the elongate member and encompassing the second balloon tocapture any radioactive liquid escaping from the second balloon in theevent of a leak in the membrane thereof.
 18. The method of claim 17,wherein the catheter includes a pair of blocking balloons secured to thedistal end of the elongate member at points respectively distal andproximal of the containment sheath, and the method further includes thestep of:inflating both blocking balloons before introducing saidradioactive liquid into the second balloon, to contain the radioactiveliquid in the region of the blood vessel subjected to the angioplastyprocedure in the event of a total failure of all other containmentsystems of the catheter.
 19. A method of relieving a stenosis andpreventing restenosis of a selected portion of a blood vessel in apatient, such as a coronary artery, comprising the steps of:selecting acatheter comprising a flexible elongate member having a proximal end, adistal end, an angioplasty balloon secured to said distal end, and acontainment membrane substantially surrounding said angioplasty balloonto retain fluid leaking from the angioplasty balloon in the event ofrupture thereof, said catheter being sized and of sufficient flexibilityfor introduction into the selected portion of the blood vessel;advancing said catheter along a cardiovascular lumen of the patientuntil said angioplasty balloon is disposed in the selected portion ofthe blood vessel; inflating said angioplasty balloon through an openingadjacent the proximal end of the catheter and along a first lumencommunicating with the angioplasty balloon, sufficiently to relieve astenosed region of said blood vessel; deflating said angioplasty balloonthrough said first lumen in the catheter after relieving said stenosedregion, and then re-inflating the angioplasty balloon with a liquidcontaining a radioactive material through said proximal opening and thefirst lumen for performing intravascular radiotherapy of the bloodvessel along at least the portion thereof where the stenosed region hasbeen relieved; maintaining the angioplasty balloon inflated with saidliquid for a predetermined period of time sufficient to deliver aneffective dose of radiation to the blood vessel wall in the selectedportion of the blood vessel; withdrawing said liquid from saidangioplasty balloon through said first lumen in the catheter immediatelyafter said predetermined period of time has elapsed to allow theangioplasty balloon to collapse; and withdrawing said catheter from thepatient.
 20. The method of claim 19 wherein the step of re-inflating theangioplasty balloon is performed to a pressure which is less than theinflation pressure used for the angioplasty balloon during the step forrelieving the stenosed region of the blood vessel.
 21. The method ofclaim 20, further including the step of:inflating said containmentmembrane with a radio-opaque contrast medium to verify the integrity ofthe containment membrane prior to re-inflating the angioplasty balloonwith the radioactive liquid.